1. Field of the Invention
The present invention relates to an abrasive means for grinding samples during supply of a liquid lubricant and including a binding agent layer having grains of a grinding agent and a soluble material incorporated therein.
2. The Prior Art
In the art of materialography (the study of materials, e.g. metals) it is common practice to grind and/or polish the samples before performing the various analyses on them. For most analyses, it is crucial that the surface of the sample to be analyzed is as smooth and/or planar as possible.
The prior art abrasive means and in particular the abrasive means typically used for grinding materialographic samples, such as grinding paper, normally have the drawback that they initially produce a relatively strong removal of material, and that the removal of material is reduced significantly over time as the abrasive grains are worn down or loosened from the binding agent layer.
It has been attempted to obtain a more uniform removal of material over time by using a layer of binding agent which during the advancing of the grinding process is partly decomposed, thus exposing new grinding grains.
Accordingly, U.S. Pat. No. 3,925,034 discloses a process for the preparation of abrasive disks comprising an abrasive layer of grinding grains, a resin based binding agent and a voluminously substantial amount of porous resin beads, said beads creating cavities in the abrasive layer due to thermal melting, thus causing the worn down grinding grains to be loosened at a suitable rate during the grinding process.
U.S. Pat. No. 5,549,961 discloses grinding means comprising an abrasive layer consisting of a binding agent, grinding grains and a plasticizer, which facilitates the removal of worn down grinding grains and the exposure of new ones.
EP 0 486 308 discloses grinding means comprising a layer of a binding agent comprising incorporated grinding grains covered with a coating produced from a mixture of an epoxy resin, an emulsifier for the epoxy resin, a curing agent, a grinding aid dispersed in the epoxy resin and water. As examples of grinding aids are mentioned waxes, organic halogen containing compounds, halogen salts, metals and metal alloys.
In some grinding and/or polishing processes, it is common to supply a lubricant during the process. The purpose of supplying a lubricant during the grinding process is partly to reduce friction, partly to remove frictional heat which arises during the grinding and partly to remove the material which is removed from the treated sample and fragments of grinding grains. As lubricant water or mixtures of water with water miscible alcohols is typically used, and the lubricant is typically supplied continuously during the grinding process.
U.S. Pat. No. 5,476,416 discloses a flexible grinding stone comprising a flexible plastic material having mixed therewith a powder synthetic detergent and an abrasive such as silica sand and calcium carbonate composed of grains from 3 to 50 xcexcm, and capable of simultaneously removing minute protrusions and stain from coated surfaces. The powder synthetic detergent is present in the form of particles having a particle size of 30 to 1500 xcexcm, and it is mentioned that the detergent particles can dissolve in water optionally supplied during the grinding process thus exposing fine abrasive particles from within the grinding stone. According to U.S. Pat. No. 5,476,416 the detergent particles are most effective when applied in an amount of 10-20 weight-% and having a particle size from 100 to 1500 xcexcm.
Flexible grinding stones are unfortunately not expedient for all grinding purposes. Particularly when the objective is to obtain an extremely planar or smooth surface, e.g. in connection with material analysis or precision grinding, it is preferable that the resilience of the grinding means is relatively low. If the grinding means is too flexible it will also potentially be worn down unevenly eventually leading to an uneven treatment of the sample to be ground, which in most cases is highly unacceptable.
Furthermore, the use of a detergent in a grinding process is generally undesirable because it can dissolve in certain binding agents, thus losing the effect and even possibly impair the binding agent properties. In addition, particles consisting of a detergent can be too soft and/or brittle thus being compressed too easily during the grinding process.
Accordingly there persists a need for an abrasive means capable of providing an even abrasion over time as well as over the entire grinding surface of the means and without having the above mentioned deficiencies.
This objective is obtained by the abrasive means according to the invention, wherein the binding agent layer includes discrete particles incorporated therein including one or more organic acids soluble in the lubricant and having a particle size from 5 to 250 xcexcm.